Genetic Sports Gene ACTN3 DNA Test Genetic Sports Gene ACTN3 DNA Test is the gene responsible for making a protein called alpha-actinin-3 that is found in skeletal muscle. Just about all body movement from nodding your head to running is caused by skeletal muscle contraction. This muscle is composed of two types of fibres: slow twitch and fast twitch. Whereas slow twitch muscle fibres are very efficient and can work continuously for long periods, it is your fast twitch fibres that are responsible for generating the short, explosive bursts of power needed in activities such as sprinting and weight lifting. The alpha-actinin-3 protein is found almost exclusively in fast twitch muscle fibres